From EP-A-0 418 151 a cellulose sponge produced from viscose is known. According to this known process, wood pulp is converted into the xanthate, the xanthate is mixed with a porophore and fibres, whereafter particles of an absorbing polymer coated with a polymer layer are added. Afterwards, the xanthate is regenerated using an acid or a base, and the regenerate is washed and bleached.
A disadvantage of this process is that due to the by-products of the viscose process its environmental impact creates problems to be solved.
For some decades there has been searched for processes able to substitute the viscose process today widely employed. As an alternative which is interesting for its reduced environmental impact among other reasons, it has been found to dissolve cellulose without derivatisation in an organic solvent and extrude from this solution moulded bodies, e.g. fibres, films and other moulded bodies. Fibres thus extruded have received by BISFA (The International Bureau for the Standardization of man made fibers) the generic name Lyocell. As an organic solvent, BISFA understands a mixture of an organic chemical and water.
It has turned out that as an organic solvent, a mixture of a tertiary amine-oxide and water is particularly appropriate for the production of cellulose moulded bodies. As the amine-oxide, primarily N-methylmorpholine-N-oxide (NMMO) is used. Other amine-oxides are described e.g. in EP-A-0 553 070. A process for the production of mouldable cellulose solutions is known e.g. from EP-A-0 356 419. The production of cellulose bodies using tertiary amine-oxides generally is referred to as amine-oxide process.
In EP-A-0 356 419, a process for the production of cellulose solutions is described, wherein as a starting material among other substances a suspension of cellulose in liquid, aqueous N-methylmorpholine-N-oxide (NMMO) is used. This process consists in transforming the suspension in a thin-film treatment apparatus in one single step and continuously into a mouldable solution. Finally. the mouldable solution is spun into filaments by means of a forming tool such as a spinneret and the filaments are conducted through a precipitation bath.
The cellulose is precipitated from the solution in an aqueous spinning bath. During this process, amine-oxide accumulates in the spinning bath. The content of amine-oxide in the process waters produced amounts to up to 30% by weight. For the economy of the amine-oxide process it is of vital importance to recover and reuse the amine-oxide nearly completely.
In the literature, virtually nothing is known about the production of a cellulose sponge according to the amine-oxide process. Only in 1988 it was reported that a new process for the production of cellular cellulose, which is similar to sponges, from a solution of cellulose in an aqueous tertiary amine-oxide was searched. It is further reported that a number of parameters, whereof the water content is of foremost importance, influences the production, and that the products obtained are similar to those produced from viscose (Peguy: "New Materials from Cellulose or Lignocellulose Solutions in Amine Oxides"; Proceedings of the Nisshinbo International Conference in Cellulosics Utilization in Near Future, Tokyo 1988, pages 19-24, Elsevier Applied Science). However, a reproducible teaching for the production of sponges from the cellulose solutions cannot be deduced from this literature.
It is the object of the invention to provide a cellulose sponge which is to be produced according to the amine-oxide process.